NbS Triple Win Toolkit: Economics and Finance 79 Difficulties assessing NbS costs and benefits Benefits Evidence from NbS case studies illustrates not only the breadth of benefits that can achieved by NbS projects across the triple win objectives, but also the depth of benefits per objective. The 12 case studies exemplify how NbS can achieve a wide breadth of benefits simultaneously. To address the breadth of social benefits NbS can provide, the Green Book distinguishes between three different classifications of benefits, primarily based on the ability to quantify and/or monetise the benefit18. These are: Monetisable benefits, including cash benefits. These are benefits which can be valued with market or non-market prices. Some ofthese can be cash-releasing, meaning that they correspond to returning real monies into the hands of their beneficiaries. Quantifiable but not monetisable benefits. These are benefits which can be quantified (e.g. extent of land cover protected per hectare) but are difficult to value credibly in project appraisal. Qualitative unquantifiable benefits. These are benefits which are difficult to quantify or value, and which are often discussed descriptively in the context of wider project benefits Of the benefits which NbS deliver, only three are regularly monetised and included in economic analysis of NbS. GHG emissions sequestered or avoided. Where calculated, this can generate large benefit-cost ratios in favour of intervention due to both the high social cost of carbon and potentially large areas of carbon sinks available for protection and enhancement. This is not always fungible; carbon markets and offsetting credit schemes are required to generate cash flow. Increasing income. Higher incomes can stem from climate-resilient crops generating more reliable income streams, higher prices for new higher yielding crop varieties, improved productivity of fisheries or associated land. Increasing incomes arises from either higher revenues or lower input costs. Avoided costs. These could arise from reduced risks to downstream areas from protecting upper catchment, reduced flood damage alongside rivers, reduced economic impacts of crop losses due to diversification on farms, or reduced cost of inputs due to intervention. As discussed, many of the social, poverty reduction and biodiversity benefits captured and discussed in economic assessments are described as additional co-benefits of NbS projects and often afforded inappropriate weight in the economic argument for intervention in comparison with monetisable benefits. This is a weakness if decision-makers rely on benefit-cost ratios exceeding an arbitrary threshold as it encourages potentially disproportionate attention to be afforded to those benefits which are easy to monetise and potentially biases the choice of projects (and therefore specific communities) which display these characteristics. It also risks precluding potentially successful NbS projects which deliver strategically across the triple win but do not deliver high benefit-cost ratios or cost-effectiveness estimates. Since the qualitative benefits are numerous, understanding, recording and continuing attempts to monetise these in a standardised and comparable manner is critical for credibly assessing the true social value for money assessments of NbS projects. With the exception of activities which directly improve local incomes, many of the poverty reduction and biodiversity benefits are difficultto define, monitor, quantify and subsequently value. In particular,